Microscopic investigation of the reasons for field-dependent changes in the properties of magnetic hybrid materials using X-ray microtomography

Magnetic hybrid materials, i.e. materials containing magnetic particles as magnetoactive component in a non-magnetic matrix, can be controlled concerning their properties by means of moderate magnetic fields. The magnetic field-driven change in their properties is a result of the complex interaction of the magnetic particles and—in case of elastomers used as non-magnetic matrix—of the interaction of the particles with the surrounding matrix. These complex interactions are the major problem to achieve an understanding of magnetic hybrid materials on a level allowing tailored material production for certain application purposes. Such an understanding requires a scale bridging description of the material behaviour and of the resulting magnetically induced effects. In this context, the term scale bridging means that it is necessary to couple changes in the internal structure of a magnetic hybrid material, i.e. effects taking place on the scale of the magnetic particles, with macroscopic changes in its properties. Such a scale bridging understanding can not only be achieved on theoretical level. The complexity of the interparticle interaction and of the interaction of the particles with matrix as well as the vice versa coupling of both kind of interactions requires experimental data as input for theoretical approaches: moreover, such data provide a benchmark for respective predictions. Coupling magnetomechanical investigations on the macroscale with microscopic characterization using X-ray microtomography as a tool for a detailed visualization of the microstructure provides the required experimental approach to a scale bridging description of such smart materials. Within this paper, we will outline the required techniques for micro-and macroscopic investigations and will highlight the possibilities given by such an approach with a couple of examples.